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A further review of the principal structural and stratigraphic characteristics of the northwestern Colombia area, in the southern Caribbean borderland has led me to revise previous interpretations, now recognizing it as a new tectonostratigraphic province in which diapirism is the principal stress factor in modeling what here is termed the Sinú-San Jacinto terrane.Gravity loading of pelagic and hemipelagic sediments by denser turbidites triggered diapirism along the trench margins during the two principal accretionary episodes in the evolution of this terrane. The magnitude of deformation combined with uplift characterizes this diapirism as orogenic. The scales of deformation and uplift also appear directly related to the intensity of turbidite sedimentation. Lateral compressional stresses previously proposed are considered a minor contribution to the modeling of the Sinú-San Jacinto terrane.The shaping of this terrane took place in two episodes corresponding to the development of the San Jacinto and Sinú accretionary wedges. The main diapiric events of the San Jacinto belt were during Paleocene to middle Eocene and during late Eocene to early Oligocene times, and the main diapiric events of the Sinú belt were during middle Miocene and during late Miocene to early Pliocene times. Each episode of intense diapirism was followed by uplift accompanied by little deformation. The diapirism appears related to deep-sea sedimentation, whereas uplift was accompanied by shallower marine and terrestrial sedimentation. Two major unconformities are characteristic of each major diapiric event: middle Eocene and early Oligocene for the San Jacinto belt and late middle Miocene and pre-late Pliocene for the Sinú belt. The former tectonicsedimentary stages are revised, and three new names, "Sinuian," "Turbarían," and "Sincelejian," are proposed.

BackgroundMarine allopatric speciation involves interplay between intrinsic organismal properties and extrinsic factors. However, the relative contribution of each depends on the taxon under study and its geographic context. Utilizing sea catfishes in the Cathorops mapale species group, this study tests the hypothesis that both reproductive strategies conferring limited dispersal opportunities and an apparent geomorphologic barrier in the Southern Caribbean have promoted speciation in this group from a little studied area of the world.Methodology/Principal FindingsMitochondrial gene sequences were obtained from representatives of the Cathorops mapale species group across its distributional range from Colombia to Venezuela. Morphometric and meristic analyses were also done to assess morphologic variation. Along a ∼2000 km transect, two major lineages, Cathorops sp. and C. mapale, were identified by levels of genetic differentiation, phylogenetic reconstructions, and morphological analyses. The lineages are separated by ∼150 km at the Santa Marta Massif (SMM) in Colombia. The northward displacement of the SMM into the Caribbean in the early Pleistocene altered the geomorphology of the continental margin, ultimately disrupting the natural habitat of C. mapale. The estimated ∼0.86 my divergence of the lineages from a common ancestor coincides with the timing of the SMM displacement at ∼0.78 my.Main Conclusions/SignificanceResults presented here support the hypothesis that organismal properties as well as extrinsic factors lead to diversification of the Cathorops mapale group along the northern coast of South America. While a lack of pelagic larval stages and ecological specialization are forces impacting this process, the identification of the SMM as contributing to allopatric speciation in marine organisms adds to the list of recognized barriers in the Caribbean. Comparative examination of additional Southern Caribbean taxa, particularly those with varying life history traits and dispersal capabilities, will determine the extent by which the SMM has influenced marine phylogeography in the region.

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